This invention relates to draft sensing apparatus for tractors.
Tractor draft sensing apparatus are already known which include an elongated shaft having support portions for mounting in spaced fulcrum supports and end portions positioned axially outward of said support portions for mounting a pair of draft members, the arrangement being such that draft forces imposed on the shaft by the draft members cause the shaft to bend, and sensing means are arranged to produce a draft signal proportional to the amount of bending of the shaft. One example of such a system is described in U.S. Pat. No. 3,888,315.
Two problems may be experienced with draft sensing apparatus of the above type. Firstly, the apparatus may have an appreciable amount of internal friction, for example in the fulcrum supports and sensing means, resulting in the apparatus exhibiting considerable hysteresis which tends to make the apparatus imprecise in its response to changes in draft loads. Secondly, the shaft may be subjected to extremely high draft forces which may cause the tensile bending stresses induced in the shaft to approach the elastic limit of the shaft material even when the shaft is heat treated.
It is an object of the present invention to provide a tractor draft sensing apparatus which at least alleviates one or both of the above problems.